UN Secretary-General Antonio Guterres is urging nations not to damage Iran's 2015 nuclear agreement with world powers because of concerns they may have with Iran's nonnuclear military activities in the Middle East.

"Issues not directly related to the [nuclear deal] should be addressed without prejudice to preserving the agreement and its accomplishments," Guterres said in a statement on January 17.

The deal is a "major achievement of nuclear nonproliferation and diplomacy, and has contributed to regional and international peace and security," he said.

The administration of U.S. President Donald Trump has repeatedly criticized Iran's ballistic-missile development as well as support for Syria's government in a six-year civil war and its backing of Yemeni Huthi rebels, while demanding major changes in the nuclear deal.

On January 12, Trump threatened to pull out of the deal unless it is changed to clearly prohibit ballistic-missile development, among other changes he is seeking.

Trump said he was waiving U.S. nuclear-related sanctions for another 120 days, as required under the deal in exchange for curbs on Iran's nuclear activities.

But he said was doing so for the "last time" to give U.S. and European negotiators a "last chance" to enact measures to fix what he called the deal's "disastrous flaws."

Iran has ruled out any changes in the agreement, maintaining that Trump's demands violate terms of the deal sealed by the administration of former U.S. President Barack Obama and signed by Britain, France, Germany, China, and Russia.

While the Trump administration insists that Iran's testing of ballistic missiles that are capable of carrying nuclear weapons violates the "spirit" of the nuclear accord, Guterres noted that the International Atomic Energy Agency has repeatedly concluded that Iran is fulfilling its side of the agreement.